Aircraft manufacturing processes have relied on mechanical fixtures to hold components being assembled and to align tools that are performing manufacturing operations on the components. However, such fixtures are not only costly to design and build, but are often specific to a particular model or variation of that component, requiring multiple fixtures to be designed, built, stored, and retrieved for use.
Increasingly, robots are being used to perform manufacturing functions that previously required such mechanical fixtures. However, the accurate location of a tool may rely on fiducial marks such as features or indices in the component that can become obscured as fillers or coatings are subsequently applied.
Fiducial marks are frequently used by machine vision systems to register tools. However, fiducial marks applied to individual piece parts or subassemblies during their manufacture may have one or more of the following deficiencies:
1) When added at the piece-part stage, the marks cannot be placed in locations that compensate for future tolerance buildup that may occur as a result of subsequent assembly steps. This results in a mark being placed within specification in the piece part's coordinate system but does not accurately represent a position in the assembly's coordinate system.
2) Placement of the fiducial markers adds a step to the creation of the piece-part.
3) The fiducial marker itself may need to withstand subsequent process steps such as annealing so use of a specialized compound could be necessary for the marker to survive certain process steps.
4) The material used to place the fiducial marker must be approved for any applicable regulatory or process standards.